Millimeter wave generator



March 31, 1-953 B. D. KUMPFER 2,633,556

. MILLIMETER WAVE GENERATOR Filed Aug. 2, 1951 FIG. I

INVENTOR.

BEVERLY D. KUMPER Patented Mar. 31, 1953 MILLIMETER WAVE GENERATORBeverly D. Kumpfer, Spring Lake Heights, N. J., assignor to the UnitedStates of America as represented by the Secretary of the ArmyApplication August2, 1951, SeriallNo. 240,023

Claims. (Cl. 315-40) Thejinvention described herein may be manufacturedand'used by or for the Government for governmental purposes, without thepayment of any royalty thereon.

.The present invention relates to electron discharge devices of themagnetron type and more particularly to magnetrons for generatingelectrical oscillation having a wavelength of a few millimeters or less.

In a recent electronic development, the use of a metallic resonantstructure in the amplifying mechanism of travelling wave amplifier tubeshave been eliminated by employing two interacting electron streamstravelling at different velocities. For a description and illustrationof this development, reference is made to the publication of Proceedingsof the I. R. E. of January 1949 and to the article entitled TheElectron-WaveTube by Andrew V. Haefi'.

The most serious obstacle for employing magnetrons for generatingoscillations of millimeter wavelength is the apparent necessity to use aplurality of metallic resonant structures of very small dimensions. Thisrequirement arises from the fact that magnetron anode structures have tobe arranged so that kinetic energy of electrons can be eflicientlyconverted into the energy of the high frequency electric fields whichare supported by these resonant structures. Because of the. requiredreduction in size when operating-at millimeter wavelength, the usefuloutput power at millimeter wavelengths of conventional mag- .netrons isgreatly reduced even when maximum emission current densities areapproached. j "The. present invention contemplates and has as a primaryobject the provision of a magnetron tube of novel design capable ofgenerating electrica1 oscillations of millimeter wavelength by utilizingtwo interacting electron streams travelling at different angularvelocities. f It is a further object of my invention to provide amagnetron wherein the usual plurality .of resonant circuits iseffectively replaced by a system of two rotating electron streams whichinteract with each other. --In accordance with the invention, amagnetron generator comprises a cylindrical anode anda pair ofcathodescentrally and axially positioned .within said anode.

For a better understanding of. the invention,

together with other and further objects thereof,

Each cathode isat a discretepotential with respect to the anode toproduce two admixed rotating space clouds traLvel- (Granted under Title35, U. S. Code (1952),

sec. 266) reference is had to the following description taken inconnection with the accompanying drawing in which:

Figure 1 is a longitudinal sectional view taken substantially throughthe center of a magnetron made in accordance with the principles of mypresent invention.

Figure 2 is a transverse sectional view taken along line 22 of Figure 1;

Figure 3 illustrates another embodiment of the cathode structureemployed in Figure 1; and

Figure 4 is a fragmentary view in cross section illustrating anotherembodiment of the single resonant structure employed in Figure 1.

Referring now to Figures 1 and 2 of the drawing, there is shown amagnetron 2 comprising an evacuated tubular anode structure 4 made of acylinder of conducting material, such as copper. The upper and lowerends of cylindrical anode 4 are closed by upper and lower annular endplates 6 and 8 respectively. The end plates are formed of a suitableconducting material such as copper and are hermetically sealed into the.ends of anode 4. Depending outwardly from the inner periphery of upperend plate 6 and rigidly brazed thereto, is tubular sleeve I0, the upperend of which is provided with a glass seal l2 for sealing the dischargedevice after evacuation. Similarly, tubular sleeve [4 depends outwardlyfrom the inner periphery of lower end plate 8 and is provided with glassseal 16.

Centrally and axially positioned within cylin} indirectly heated type,which are identical in construction and axially aligned. Cathode l8,hereinafter referred to as the upper cathode, comprises a cylindricalelectronically conductive sleeve 22, preferably made of nickel," Saidsleeve is coated externally with an electron emissive material as at 24.Disc-like end shield 26, here'- in conveniently integral with cathodesleeve 22, is provided proximal end plate 6, to'prevent emittedelectrons from being DrQject'ed outwardly toward said end plate. As ameans for supporting upper cathode I8 in position within the tube, thereis provided a tubular Kovar{ member 28 whichisaxially aligned withtubular sleeve Ill. As illustrated, one end of tubular member ZLis.welded to end shield 26.

A'hea'ter so, which is positioned within ,u'pper cathode l8 and whichis' energized by means of a heating battery 32, serves to maintaincoated surface 24 at an emitting temperature. One terminal of thecathode heating element is connected to Kovar member 28 by beingconnected to .cathode sleeve 22 and the other terminal is connected tolead-in conductor 34 which extends through aperture 36 of end shield 25,and through "Kovar tubular member 28. A glass seal 3 between lead-inconductor 34 and tubular member 23 maintains the structure vacuum tight.

Cathode 2%, hereinafter referred to as the lowor cathode, is identicalin construction with up per cathode l8 and is similarly provided with acylindrical conductive sleeve 4% which is terminated proximal end plate8 by disc-like end shield 42. Like upper cathode l8, sleeve 43 is coatedwith an electron emissive material as at- A 44. Tubular Kovar member 43is provided to support lower cathode 2G in position and maintain it inspaced relationship with upper cathode I 8. As shown, tubular member 45is axially plate 8. A heater 41, which is similar to heater 30 supra, ispositioned within lower cathode 28 to maintain coated surface 44 at an"emitting temperature and is energized by means of heating battery 48through lead-in conductor 58. Glass seal 52 between lead-in conductor5!! and tubular member 46 maintains the structure vacuum tight.

Cathode i3 is maintained at a negative potentialEi with respect to-anode4 by means of an appropriate voltage source 54 which is applied tocathode is by tubular member 28 through glass seal l2. Similarly,cathode 26 is maintained at a negative potential E2 with respect toanode 4 by means of voltage source 58 which is applied to cathode 2%through tubular member 55 and glassseal iii. B; may be slightly higherthan E2, or vice versa. Cylindrical anode 4 is provided with a slot '58open at both ends and axially parallel to the axis of said cylindricalanode; The depth of slot 58 radially fromthe inner periphery of anode 4is preferably chosen to be eifectively one-quarter wavelength of theoperating frequency so as to provide a resonant cavity therefor. Ifdesirable, slot 58 may be a closed end resonator as shown at 58' inFigure 4, the axial length thereof being effectively one-half wavelengthto form a resonantwaveguide sectionat the operating frequency.

In order to take power from the magnetron,

cylindrical anode 4 is. provided with a] second, radially disposed,coupling. slot 60, which is coupled and suitably matched to waveguide182. The depth of slot E0 outwardly from the inner .pe-

riphery of anode 4 is preferably chosen to be effectively one-halfwavelength of the operating 'frequency' As shown, coupling slot 50 isopen .at both ends and is axially parallelto the axis .ofcylindricalanode 4. A glass Window 64 sealed into the waveguidemaintains the structure vacuum tight. Resonant slot 58 and output slotBil may be positioned, relative to each other along '65 and 66 whichmaybe energized by any of the :means well known in the art not shown,Preferably, the flux lines should be concentrated in the interactionspace 68, between cathodes l8 and 20 and cylindrical anode 4.

4 In operation, the discrete electron space clouds from the two cathodesare propagated in the interaction space at discrete angular velocitieswhich may be calculated from the formula wherein E is the intensity ofthe electric field in the space between the anode and the cathode and Bthe value of the constant magnetic field. Thus the' electron space cloudfrom upper cathode [8 travels with an angular velocity and the electronspace cloud from lower cathode 20 travels with an angular velocity Bothelectron streams are bunched or. density modulated by the singleresonant circuit 58 in anode 4 in accordance with conventional'mag-J-netron operation. The admixed bunched streams then rotate around theinteraction space and interact with each other. As ex lained by Haefi inthe hereinabove mentioned article, the lower velocity stream gainsenergy from. the higher velocity stream in'the process of the spacecharge interaction without the use of a continuous resonant structure. Aportion of the am:- plified energy is coupled out by output couplingslot 65 and theresidual energy in the two interacting streams is allowedto feed back around the anode structure to provide regeneration. Sinceonly one resonant structure is required rather than a plurality thereof,the power output at millimeter wavelength operation is greatlyincreased. i Y Figure 3 illustrates two .identical helically woundfilaments and 12 of the directly heated type which may be utilized inplace ofthe cylindrical cathodes [8' and 20. Filaments Ill and 12 areinsulated with respect to each other and may be coaxially mounted withinand axially aligned ,with cylindrical anode 4. Voltage E1 isappliedbetween cathode ill and cylindrical anode 4 and voltage E2 is appliedbetween cathode 12 and said anode. The windings of the helically-shapedfilaments are so arranged that corresponding windings such as M and 16are superimposed.

While there have been described what at pres.- ent are considered to bethe preferred embodimerits of the invention, it will be understood bythose'slcilled in the art that various changes and modifications may bemade herein without de xparting' from the invention, and it is,therefore, aimed in the appended claims to cover all such modificationsand changes as fall within the spirit and scope of the invention.

What is claimed is: v

1". An electron discharge device of the magnetron type comprisingacylindrical anode including a pair of radical slots, a cathode assemblycentrally positioned within said anode comprisiing axially spaced andelectrically independent first and second electron emitting surfaces;said electron emitting surfaces being axially aligned with said anodefor supplying electrons to the space between saidanode and said firstand second electron emitting surfaces to produce aflrst and secondelectron space cloud, means supporting said electron'emitting surfacesin said axial spaced relationship, magnetic means adjacent said anodefor producing a constant axial mag netic field in the space between saidelectron emitting surfaces and said anode, means in cir cuit with saidanode and said first electron emitting surface for establishing a firstelectric field perpendicular to and cooperable with said magnetic fieldwhereby said first electron space cloud is rotated at a firstpredetermined angular velocity, means in circuit with said anode andsaid second electron emitting surface for establishing a second electricfield perpendicular to and cooperable with said magnetic field wherebysaid second electron space cloud is rotated at a second predeterminedangular velocity.

2. An electron discharge device of the magnetron type comprising acylindrical anode including a pair of radial slots, said slots beingopen at both ends and longitudinally parallel to the axis of said anode,a cathode assembly centrally positioned within said anode comprisingaxially spaced and electrically independent first and second conductivecylindrical sleeves, each of said sleeves being coaxial with saidcylindrical anode, means supporting said sleeves in said axial spacedrelationship, magnetic means ad =jacent said anode for producing aconstant axial magnetic field in the space between said anode and saidcathode assembly, means included in said cathode assembly for supplyingelectrons to the space between said anode and said first and secondsleeves to produce a first and second electron space cloud, meansconnected between said first sleeve and said anode for establishing afirst electric field perpendicular to and cooperable with said magneticfield whereby said first electron space'cloud is rotated at a firstpredetermined angular velocity, means connected between said secondsleeve and said anode for establishing asecond electric fieldperpendicular to and cooperable with said magnetic field Whereby saidsecondelectron space cloud is rotated at a second predetermined angularvelocity.

3. A magnetron device comprising a cylindrical anode including a pair ofradial slots, said slots being open at both ends and longitudinallyparallel to the axis of said anode, a cathode assembly centrallypositioned within said anode comprising axially spaced and electricallyindependent first and second conductive cylindrical sleeves,

each of said sleeves being coaxial with said anode. means supportingsaid sleeves in said axial spaced relationship, magnetic means adjacentsaid anode for producing a constant axial magnetic field in the spacebetween said anode and said cathode assembly, means included in saidcathode assembly for supplying electrons to the space between said firstand second sleeves and said anode to produce a first and second electronspace cloud, 2. first source of direct-current potential coupled betweensaid first sleeve and said anode to establish an electric fieldperpendicular to and cooperable with said magnetic field whereby saidfirst space cloud is rotated at a first predetermined angularlyvelocity, and a second source of direct-current potential coupledbetween said second sleeve and said anode to establish an electric fieldperpendicular to and cooperable with said magnetic field whereby saidsecond space cloud is rotated at a second predetermined angularvelocity.

4. The electron discharge device set forth in claim 1 wherein the radialdepth of one of said slots is substantially wavelength of the operatingfrequency and the radial depth of the other of said slots issubstantially wavelength of the operating frequency.

5. The electron discharge device set forth in claim 1 wherein said slotsare closed at both ends and are substantially wavelength of theoperating frequency.

BEVERLY D. KUMPFER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,409,038 Hansell Oct. 8, 19462,423,716 McArthur July 8, 1947 2,429,291 Okress Oct. 21, 1947 2,438,194Steele, Jr. et a1 Mar. 23, 1948 2,443,179 Beniofi June 15, 19482,452,077 Spencer Oct. 26, 1948 2,493,423 Spooner et al Jan. 3, 19502,513,933 Gurewitsch July 4, 1950

